My biggest reason for twin diesels is that we have strong currents , even whirlpools in desolation sound , dont I need power?
NO.
If you want the power to go fast that's fine. But do not count on the power to keep you out of trouble in the passes with fast , strong currents.
What you do need to do is get ahold of the tide and current tables and learn to use them so you avoid those currents. As you gain experience with the currents you can play around a bit but even so they deserve respect.
I have known people with the attitude that they can power through any current. The only trouble was the currents did not understand or agree with their thinking.
Nobody got killed but there were injuries and boat damage. Also wood can be hidden in the turbulent water. At slack water, which is when you should aim for, that same wood will usually be visible unless it is a true deadhead.
Unfortunately Canada no longer publishes the Tide and Current tables. They do offer them for free online and/or for you to print. I have downloaded them but finally broke down and purchased the Ports and Passes book which I had resisted for the last MANY years.
I would suggest you download the Cdn, version and learn to use the tables for nothing other than the effort. When you get your boat then buy the P & P book.
It is not just the currents that are important. You also need to understand the tides and how to use those tables or you may be stranded/beached or run over something you need not have.
Lots of anchorages are useable but only if you understand the tide tables.
Last and I will leave. The faster you go the less time you have to spot floating hazards and if/when you argue with something the damage will be more severe.